1. Technical Field
This invention relates to apparatus for sensing the temperature of fluid flow within a pipe in general, and to apparatus that can be used to non-intrusively sense fluid flow temperature within a pipe in particular.
2. Background Information
In the oil and gas industry, there is considerable advantage in having the ability to accurately measure the temperature of a fluid within a pipe at one or more locations down within a well (xe2x80x9cdownholexe2x80x9d). Until recently, fluid temperature has typically been sensed at the top or xe2x80x9cwellheadxe2x80x9d of a well. A problem with wellhead temperature data is that it can be influenced by heat transfer between the fluid and the pipe that occurs along the length of the pipe. Another problem with wellhead temperature data is that in multi-source wells, the fluid temperature data collected at the wellhead reflects a mixture of the fluid temperatures from the different sources and yields no temperature data specific to the individual sources. Knowing the temperature at a discrete locations within the well would avoid these problems and help enable the determination of relevant information that can be used to increase the productivity and efficiency of the source or sources.
Acquiring reliable, accurate temperature data in a downhole environment is, however, a technical challenge for at least the following reasons. First, fluid flow within a production pipe is hostile to sensors in direct contact with the fluid flow. Fluids within the production pipe can erode, corrode, wear, and otherwise compromise sensors disposed in direct contact with the fluid flow. In addition, the hole or port through which the sensor makes direct contact, or through which a cable is run, is a potential leak site. There is great advantage in preventing fluid leakage out of the production pipe. Second, the environment in most wells is harsh, characterized by extreme temperatures, pressures, and debris. Extreme temperatures (hot or cold) can disable and limit the life of electronic components, particularly those in contact with the fluid. Extreme temperature gradients between the fluid flow and the ambient environment can also undesirably influence the accuracy of a temperature sensor. An unprotected sensor disposed outside of a production pipe, for example, will likely be subject to thermal gradients between the fluid flow and the ambient environment; e.g., a subsea well application can have production pipe fluid temperatures up to and beyond 200 degrees Celsius (xc2x0 C.) and ambient ocean environment temperatures of approximately 2-3xc2x0 C. In such an instance, the unprotected sensor may be influenced more by the ambient temperature than by fluid temperature inside the production pipe. Sensors disposed outside of the production pipe may also be subject to debris and environmental materials such as water (fresh or salt), mud, sand, etc. Third, the well environment makes it inconvenient and/or expensive to access most sensors once they have been installed and positioned downhole.
What is needed, therefore, is a reliable, accurate, and compact apparatus for measuring temperature within a pipe, one that can measure the temperature of a fluid within a pipe in a non-intrusive manner, one that is operable in a well environment characterized by extreme temperatures and pressures and the presence of debris, and one that is not likely to need replacement or recalibration once installed.
It is, therefore, an object of the present application to provide an accurate, reliable, and compact apparatus for measuring fluid temperature within a pipe that can perform in a well environment in a non-intrusive manner.
According to the present invention, an apparatus for sensing the temperature of a fluid being drawn from a well includes a pipe having a wall, a sensor mounted on the outer surface of the pipe wall, a thermal insulator, and a housing attached to the pipe that encloses the sensor and the insulator. The fluid to be sensed is drawn from the well through the pipe. The thermal conductivity of the pipe wall is substantially greater than that of the insulator.
In a preferred embodiment, the housing forms a pressure vessel with the pipe, and the insulator and the sensor are disposed within the pressure vessel. Gases such as air, nitrogen and argon are favorable insulators, although other insulators can be used alternatively. The pressure of the gas within the pressure vessel can also be varied to suit the application; e.g., lesser or greater than ambient. The sensor mounted on the pipe and housed within the sensor housing can be any type of thermal sensor capable of sensing fluid temperature through the wall of the pipe with adequate sensitivity. In the most preferred embodiment, the sensor is a fiber Bragg Grating (FBG) type optical sensor.
An advantage of the present invention is that a compact apparatus for measuring temperature within a well is provided. The present invention fits compactly on the exterior of the production pipe and is therefore easily placed within the casing of a well.
Another advantage of the present invention is that it measures temperature of the fluid in a non-intrusive manner. The sensor mounted on the outer surface of the pipe does not require an opening extending into fluid flow path. As a result, a potential leak path into or out of the fluid flow path is eliminated. In addition, the sensor is protected from the fluid flow within the pipe.
The present sensor is also protected from the environment outside of the production pipe by the housing. The housing protects the sensor from fluid and debris that enters the annulus between the pipe and the well casing. The housing also protects the sensor by insulating it from elevated temperatures and pressures, and pressure variations present in the annulus. As a result, the present invention can use a wider variety of sensors than would otherwise be possible. In addition, in the embodiment where the sensor is disposed within a pressure vessel, the sensor is subjected to a substantially constant pressure. Variations in the pressure outside of the pressure vessel that might influence the sensor are effectively eliminated. For all of these reasons, the reliability and durability of the sensor is accordingly improved.
Another advantage of the present invention is that it has increased thermal capability over most temperature sensors currently used in a well application. The arrangement of the sensor mounted on the outer surface of the pipe where it is protected by the housing permits the use of optical sensors such as a FBG that have a thermal capacity higher than most conventional sensors used in well applications.
These and other objects, features and advantages of the present invention will become apparent in light of the detailed description of the present invention.